This invention relates to stable, macro emulsions of hydrocarbons in water derived from the Fischer-Tropsch process.
Hydrocarbon-water emulsions are well known and have a variety of uses, e.g., as hydrocarbon transport mechanisms, such as through pipelines or as fuels, e.g., for power plants or internal combustion engines. These emulsions are generally described as macro emulsions, that is, the emulsion is cloudy or opaque as compared to micro emulsions that are clear, translucent, and thermodynamically stable because of the higher level of surfactant used in preparing micro-emulsions.
While aqueous fuel emulsions are known to reduce pollutants when burned as fuels, the methods for making these emulsions and the materials used in preparing the emulsions, such as surfactants and co-solvents, e.g., alcohols, can be expensive. Further, the stability of known emulsions is usually rather weak, particularly when low levels of surfactants are used in preparing the emulsions.
Consequently, there is a need for stable, macro emulsions that use less surfactants or co-solvents, or less costly materials in the preparation of the emulsions. For purposes of this invention, stability of macro emulsions is generally defined as the degree of separation occurring during a twenty-four hour period, usually the first twenty-four hour period after forming the emulsion.
In accordance with this invention a stable, macro emulsion wherein water is the continuous phase is provided and comprises Fischer-Tropsch process water, a hydrocarbon and a non-ionic surfactant. Preferably, the emulsion is prepared in the substantial absence, e.g., xe2x89xa62.0 wt %, preferably xe2x89xa61.0 wt % or complete absence of the addition of a co-solvent, e.g., alcohols, and preferably in the substantial absence of co-solvent, that is, Fischer-Tropsch process water may contain small amounts of oxygenates, including alcohols; these oxygenates make up less oxygenates than would be present if a co-solvent was included in the emulsion. Generally, the alcohol content of Fischer-Tropsch process water is less that about 2 wt % based on the process water, more preferably less than about 1.5 wt % based on the process water.
The macro-emulsions that are subject of this invention are generally easier to prepare and more stable that the corresponding emulsion with, for example, distilled water or tap water. Using the Fischer-Tropsch process water takes advantage-of the naturally occurring chemicals in the Fischer-Tropsch process water to reduce the amount of surfactant required to prepare stable emulsions.
The Fischer-Tropsch process can be described as the hydrogenation of carbon monoxide over a suitable catalyst. Nevertheless, regardless of the non-shifting catalyst employed, water is a product of the reaction.
2nH2+nCOxe2x86x92CnH2n+2+nH2O
The Fischer-Tropsch process -water, preferably from a non-shifting process, separated from the light gases and C5+product can generically be described as (and in which oxygenates are preferably xe2x89xa62 wt %, more preferably less than about 1 wt %):
The Fischer-Tropsch process is well known to those skilled in the art, see for example, U.S. Pat. Nos. 5,348,982 and 5,545,674 incorporated herein by reference and typically involves the reaction of hydrogen and carbon monoxide in a molar ratio of about 0.5/1 to 4/1, preferably 1.5/1 to 2.5/1, at temperatures of about 175-400xc2x0 C., preferably about 180xc2x0-240xc2x0, at pressures of 1-100 bar, preferably about 10-50 bar, in the presence of a Fischer-Tropsch catalyst, generally a supported or unsupported Group VIII, non-noble metal, e.g., iron, nickel, ruthenium, cobalt and with or without a promoter, e.g. ruthenium, rhenium, hafnium; platinum, palladium, zirconium, titanium. Supports, when used, can be refractory metal oxides such as Group IVB, e.g., titania, zirconia, or silica, alumina, or silica-alumina. A preferred catalyst comprises a non-shifting catalyst, e.g., cobalt or ruthenium, preferably cobalt with rhenium or zirconium as a promoter, preferably cobalt and rhenium supported on silica or titania, preferably titania. The Fischer-Tropsch liquids, i.e., C5+, preferably C10+ are recovered and light gases, e.g., unreacted hydrogen and CO, C1 to C3 or C4 and water are separated from the hydrocarbons. The water is then recovered by conventional means, e.g., separation.
The emulsions of the invention are formed by conventional emulsion technology, that is, subjecting a mixture of the hydrocarbon, water and surfactant to sufficient shearing, as in a commercial blender or its equivalent for a period of time sufficient for forming the emulsion, e.g., generally a few seconds. For general emulsion information, see generally, xe2x80x9cColloidal Systems and Interfacesxe2x80x9d, S. Ross and I. D. Morrison, J. W. Wiley, NY, 1988.
The hydrocarbons that may be emulsified-by the Fischer-Tropsch process water include any materials whether liquid or solid at room temperature, and boiling between about C4 and 1050xc2x0 F.+, preferably C4-700xc2x0 F. These materials my be further characterized as fuels: for example, naphthas boiling in the range of about C4-320xc2x0 F., preferably C5-320xc2x0 F., water emulsions of which may be used as power plant fuels; transportation fuels, such as jet fuels boiling in the range of about 250-575xc2x0 F., preferably 300-550xc2x0 F., and diesel fuels boiling in the range of about 250-700xc2x0 F., preferably 320-700xc2x0 F.
The hydrocarbons may be obtained from conventional petroleum sources, shale (kerogen), Fischer-Tropsch hydrocarbons, tar sands (bitumen), and even coal liquids. Preferred sources are petroleum, kerosene and Fischer-Tropsch hydrocarbons that may or May not be hydroisomerized.
Hydroisomerization conditions for Fischer-Tropsch derived hydrocarbons are well known to those skilled in the art. Generally, the conditions include:
Catalysts useful in Hydroisomerization are typically bifunctional in nature containing an acid function as well as a hydrogenation component. A hydrocracking suppressant may also be added. The hydrocracking suppressant may be either a Group 1B metal, e.g., preferably copper, in amounts of about 0.1-10 wt %, or a source of sulfur, or both. The source of sulfur can be provided by presulfiding the catalyst by known methods, for example, by treatment with hydrogen sulfide until breakthrough occurs.
The hydrogenation component may be a Group VIII metal, either noble or non-noble metal. The preferred non-noble metals include nickel, cobalt, or iron, preferably nickel or cobalt, more preferably cobalt. The Group VIII metal is usually present in catalytically effective amounts, that is, ranging from 0.1 to 20 wt %. Preferably, a Group VI metal is incorporated into the catalyst, e.g., molybdenum, in amounts of about 1-20 wt %.
The acid functionality can be furnished by a support with which the catalytic metal or metals can be composited in well known methods. The support can be any refractory oxide or mixture of refractory oxides or zeolites or mixtures thereof. Preferred supports include silica, alumina, silica-alumina, silica-alumina-phosphates, titania, zirconia, vanadia and other Group III, IV, V or VI oxides, as well as Y sieves, such as ultra stable Y sieves. Preferred supports include alumina and silica-alumina, more preferably silica-alumina where the silica concentration of the bulk support is less than about 50 wt %, preferably less than about 35 wt %, more preferably 15-30 wt %. When alumina is used as the support, small amounts of chlorine or fluorine may be incorporated into the support to provide the acid functionality.
A preferred support catalyst has surface areas in the range of about 180-400 m2/gm, preferably 230-350 m2/gm, and a pore volume of 0.3 to 1.0 ml/gm, preferably 0.35 to 0.75 ml/gm, a bulk density of about 0.5-1.0 g/ml, and a side crushing strength of about 0.8 to 3.5 kg/mm.
The preparation of preferred amorphous silica-alumina microspheres for use as supports is described in Ryland, Lloyd B., Tamele, M. W., and Wilson, J. N., Cracking Catalysts, Catalysis; Volume VII, Ed. Paul H. Emmett, Reinhold Publishing Corporation, New York, 1960.
During hydroisomerization, the 700xc2x0 F.+ conversion to 700xc2x0 F.xe2x88x92 ranges from about 20-80%, preferably 30-70%, more preferably about 40-60%; and essentially all olefins and oxygenated products are hydrogenated.
The catalyst can be prepared by any well known method, e.g., impregnation with an aqueous salt, incipient wetness technique, followed by drying at about 125-150xc2x0 C. for 1-24 hours, calcination at about 300-500xc2x0 C. for about 1-6 hours, reduction by treatment with a hydrogen or a hydrogen containing gas, and, if desired, sulfiding by treatment with a sulfur containing gas, e.g., H2S at elevated temperatures. The catalyst will then have about 0.01 to 10 wt % sulfur. The metals can be composited or added to the catalyst either serially, in any order, or by co-impregnation of two or more metals.
The hydrocarbon in water emulsions generally contain at least about 10 wt % hydrocarbons, preferably 30-90 wt %, more preferably 50-70 wt % hydrocarbons.
A non-ionic surfactant is usually employed in relatively low concentrations vis-a-vis petroleum derived liquid emulsions. Thus, the surfactant concentration is sufficient to allow the formation of the macro, relatively stable emulsion. Preferably, the amount of surfactant employed is at least 0.001 wt % of the total emulsion, more preferably about 0.001 to about 3 wt %, and most preferably 0.01 to less than 2 wt %.
Typically, non-ionic surfactants useful in preparing the emulsions of this invention are those used in preparing emulsions of petroleum derived or bitumen derived materials, and are well know to those skilled in the art. Useful-surfactants for this invention include alkyl ethoxylates, linear alcohol ethoxylates, and alkyl glucosides. A preferred emulsifier is an alkyl phenoxy polyalcohol, e.g., nonyl phenoxyl poly (ethyleneoxy ethanol), commercially available under the trade name Igepal.
The following examples will serve to illustrate but not limit this invention.